HDL cholesterol is the good cholesterol which protects against harmful buildup in the arteries.
It is considered good to have high HDL since it can provide some protection against cardiovascular disease.
It is interesting that low levels of HDL have now been found to also be associated with poor memory (Sigh-Manoux A, et al. 2008.) The study referred to here included 3,673 male and female participants with an average age between 55-61 years. When the memory was evaluated, it was documented that a decrease in HDL over the five year follow up period was associated with a decline in memory.
This is another good reason for keeping your HDL level high. You can increase your HDL cholesterol by incorporating low glycemic index meals, avoiding trans fat and including omega 3, fat like fish oil in your diet, and also by exercising regularly.